The propulsion of devices in an aquatic medium, especially when these devices of the underwater type are moving, at least for a short while in the submerged state, requires the provision of a propulsive energy, such as electrical energy, under conditions of power, duration and modulation by successive ranges which are well determined.
This is especially the case with underwater attack, response or observation devices launched from another carrying device, such as a submarine, such launched underwater devices then being subjected to a generally brief launch stage or phase followed by a longer cruise stage or phase.
The supply of electrical energy to such launched underwater devices must then meet very specific criteria in respect of electrical power delivered and duration of delivery of this energy, in order to enable the launched underwater devices to fulfil their mission in accordance with a pre-established programme.
Under these conditions, the use of conventional electrical energy sources, such as lead accumulator batteries, cannot be accepted owing, on the one hand, to the electrical power required to ensure such a function and, on the other hand, to the inert mass necessary in order to use such conventional sources of electrical energy.
The known electrical energy sources of the prior art of the thermal cell type generally enable substantial electrical power to be delivered. However, they require the provision of substantial thermal energy in order consequently to permit the provision of electrical power.
Therefore, such sources cannot be used for mission times of aquatic devices, especially underwater devices, exceeding some tens of seconds, owing to the major difficulty encountered in providing such an amount of electrical energy beyond such a time, from thermal sources on board such devices, especially when the latter are submerged.